Background: The rising prevalence of obesity in women of childbearing age has led to increasing rates of associated comorbidities such as gestational diabetes mellitus. Moreover, obese women are more likely to develop diabetes-in-pregnancy and their offspring have a higher risk of developing obesity and metabolic disease, thereby perpetuating the current obesity epidemic. Internationally employed recommendations for weight gain in pregnancy advise differing ranges of weight gain based on pre-pregnancy weight. Weight gain outside of the guidelines compounds risk associated with maternal obesity and diabetes. Importantly, gestational weight gain is potentially modifiable. However, it is currently not known how many women in New Zealand adhere to the guidelines, as recent practice has been infrequent weighing of women during pregnancy. Once women are diagnosed with gestational diabetes mellitus, weight gain patterns may change substantially. There is a paucity of information regarding weight changes among pregnancies complicated by diabetes in New Zealand. This retrospective audit aimed to evaluate weight change among women who present to a New Zealand diabetes-in-pregnancy clinic. An additional secondary aim was to study predictors of infant birth weight in this population.

Methods: In a retrospective audit study, weight gain patterns among pregnant women with diabetes mellitus, predominantly gestational diabetes mellitus (83.3%), were evaluated. The population included women with a singleton pregnancy who presented to a New Zealand diabetes-in-pregnancy clinic during 2016. Maternal healthcare notes were reviewed to identify weight at booking, changes in weight at each clinic visit, and timing of initiating therapy. In addition, weight changes and treatment were compared to infant birth weight.

Results: 222 women presented to the clinic in 2016. 27.8% had a body mass index in the overweight and 42.4% in the obese range at booking. 30.8% gained weight within the guidelines. Women who were obese were most likely to exceed the guidelines (47.7%), whereas those with a normal weight were most likely to gain below (40.7%). Mean weight gain velocity was reduced after presenting to clinic (-0.10 kg/week), although this was not significant (95% C.I. -0.33, 0.14). Overall 79.7% received insulin treatment. Pacific Island ethnicity (87.1%) (p-value <0.04), and obesity (89.7%) (p-value <0.001) were predictive of requiring insulin treatment. Those who gained weight above the guidelines were more likely to require insulin (90.1%) than those who gained within (78.8%) or below (72.1%) the guidelines (p-value <0.025). The strongest predictor of birth weight was whether or not guidelines for gestational weight gain were met (R2=12%). Predictors of increased birth weight included total gestational weight gain (p<0.001), weight gain above the guidelines (p<0.002), increased weight at booking (p<0.02), and body mass index in the 'obese' range (p-value <0.004).

Conclusion: The majority of the study population were overweight or obese in early pregnancy, and few women adhered to the weight gain guidelines. Both increased maternal body mass index and weight gain in pregnancy above the guidelines were predictive of infant birth weight. Hence, interventions are required to reduce the prevalence of obesity in women of childbearing age, and to limit gestational weight gain among pregnancies complicated by diabetes.